Thursday, July 16, 2009

Signs of mildew

My Pinot Noir has some signs of downy mildew. It's the first time I've had to deal with this - in the past the problem has been oidium (powdery mildew), which is prevented by using elemental sulfur.

Downy mildew manifests as pale patches on the leaves, known as 'oil spots'; when you turn the leaves over, you can see the fungal infection. To prevent the mildew spreading, I've had to spray with copper (Bordeaux mixture).

4 Comments:

Bordeaux mixture very effective but can be toxic to the berries. It is important for you to clear fallen leaves off the floor of your vineyard as the fungus overwinters on them and you will have a nursery of inoculum next spring!

Flytiger is right,putting copper on will only protect against new infections, the present infection will only be stopped by a systemic fungicide (such as phosphoric acid). Copper should be applied immediately after a 10:10:24 before seeing the signs of infection by then it's too late (unless your copper has metalaxyl with it)

Jamie, given how poisonous copper is and its capacity to pollute groundwater, do you think Bordeaux mixture would be acceptable as organic, let alone biodynamic, if it wasn't just really convenient and hadn't been around for a really long time? If ICI invented it tomorrow, would it be acceptable?